1. Field of the Invention
The present invention relates to an apparatus and a method for recording or reproducing data using light.
2. Description of the Related Art
Recently, there emerges an optical recording medium that can rewrite data in high density, capable of recording and storing high quality video data and high quality audio data for a long time. For example, such medium includes a blue-ray disc.
As standardization for the blue-ray disc is under rapid process, related products are developed and brought to the market in preparation for commercialization. The blue-ray disc can store data of about 25 GB. When the blue-ray disc is manufactured in a dual layer, it can store high capacity data of about 50 GB.
Meanwhile, method of shortening a wavelength of a laser beam or increasing a numerical aperture (NA) of an objective lens have been used in order to increase a recording capacity of a recording medium.
FIG. 1 is a view of an optical system of an optical recording/reproducing apparatus according to a related art.
Referring to FIG. 1, a beam generated from a laser diode 10 is converted into a parallel beam by a collimator lens 11, passes through a beam splitter 12, and is condensed onto a recording medium 14 by an objective lens 13.
Also, a beam reflected by the recording medium 14 passes through the objective lens 13, and is reflected by the beam splitter 12, and then condensed by a lens 15 onto a light detector 16, so that the beam is detected as an electrical signal.
However, a method of shortening, at an optical system of FIG. 1, a wavelength of light in order to increase a recording capacity has reached almost limitation physically. Also, regarding a method of increasing an NA of an objective lens, it is difficult to make a great improvement using a related art far field recording method.
Accordingly, a near field recording method using a solid immersion lens is under active development, which is illustrated in FIG. 2.
Referring to FIG. 2, an SIL 22 is disposed below an objective lens 21 in the near field recording method. The SIL 22 is formed in a hemisphere shape made of a medium having a refractive index n greater than 1. The NA of the objective lens 21 is made to nxNA that is greater than 1 using the SIL 22, so that a recording capacity is increased even more.
Meanwhile, a gap between the SIL 22 and the recording medium 23 is tens of nano meters in the near field recording method. Therefore, in the case where skew or tilting is generated to the recording medium 23, the gap between the SIL 22 and the recording medium 23 cannot be maintained accurately, which may cause collision between the SIL 22 and the recording medium 23. An object of the present invention is to provide a recording/reproducing apparatus and a recording/reproducing method, capable of effectively obtaining a tilting error signal of a recording medium such that a gap between an SIL and the recording medium is maintained properly, and performing a servo operation allowing the gap between the SIL and the recording medium to be maintained properly using a tilting error signal.